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Homework Help: Gauss Law

  1. Feb 5, 2009 #1
    1. The problem statement, all variables and given/known data
    A point charge Q is placed a distance 2R above the center of an imaginary spherical
    surface of radius R. Estimate the electric flux through the sphere

    2. Relevant equations

    3. The attempt at a solution

    I think the answer is 0 as Gauss law states that the net electric flux through a closed surface that surrounds no charge is zero. In this case the charge is outside the closed surface (sphere). Am I right?
  2. jcsd
  3. Feb 5, 2009 #2


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    Homework Helper

    The total flux out of the sphere is zero all right. But I think you are supposed to find the flux from Q that passes through the sphere. Some goes in the top and then goes out the bottom, to give that total of zero.

    Find the total flux emitted by the Q. What portion of that is intercepted by the sphere? Think of the expanding sphere at the head of those flux arrows as they pass through the center of the sphere of radius R. The cross sectional area of the sphere will be some fraction of the area of that expanding sphere. A couple of area calcs will find you the answer. I see a little inaccuracy but I don't think it is a problem.
  4. Feb 5, 2009 #3
    So the answer is not 0?
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